These pearls themselves have very little value. In this case, it appears they are using pearls that may have cost as little as $35 dollars total. The 18k gold chain has far more value. Like anything though, if you use inexpensive pearls in a fashionable way, you can charge far more for them than the pearls, by themselves, are worth.

Looking at these pearls closely in the picture, they do have heavy blemishing and are treated (dyed).

Here's an example of a similar style of necklace made with AAA quality, genuine Tahitian pearls for less than twice the cost, but worth more than 10 times as much (and that is being conservative).

Tahitian Station Necklace